1. Field of the Invention
The present invention relates to a color image processing apparatus and method for color processing images.
2. Related Background Art
Hitherto, a method for projecting images on a screen or the like by utilizing an image projector such as an overhead projector (hereinafter referred to as OHP) by forming images on a transparent sheet by a full-color image forming apparatus which depends on such methods as an electrophotography, an ink-jetting, a thermotransfer recording and the like has been widely used and an importance thereof will become more serious in future.
As an OHP image sheet, a resin sheet such as an polyethylene (PET) or the like having a thickness of 100 to 150 .mu.m is widely used and a desired recorded image holding layer is provided on the resin sheet if it is required in order to improve a fixing, a holding or a resolution of images.
An image forming method which depends on the full-color image forming apparatus utilizing an electrophotographic method will be described hereinafter.
FIG. 2 is a structural view of the full-color image forming apparatus utilizing the electrophotographic method.
In the drawing, the apparatus consists of four stations for forming four color images of magenta, cyan, yellow and black. Photosensitive drums 1a to 1d are uniformly charged by primary chargers 2a to 2d and a light emitted by a semiconductor laser (not shown) driven by each color image signal is exposure scanned on the photosensitive drums 1a to 1d by a polygon mirror 17 to form a latent image. The latent image is developed by development devices 3a to 3d to form a toner image on the photosensitive drums 1a to 1d.
The toner image is formed by applying a recording material 6 in a recording material tray 60 on a transfer belt (or a transfer sheet) 8 through a pick-up roller 13a and registration rollers 13b and is then fed. A registration on the recording material 6 is synchronized. The image is thereafter multiple-transferred by thermotransfer chargers 4a to 4d, and is discharged outside an image forming apparatus upon fixing it on the recording material through a fixing roller 71 and a pressing roller 72 by means of a separation charger 14 and curvature of a transfer belt holding roller 10.
Next, there will be explained as to a fixing process.
The fixing roller 71 consists of a metallic pipe of which surface is coated by a silicone rubber and a fluoro rubber. The pressing roller 72 consists of a metallic roller of which surface is coated by the silicone rubber. A thermistor 79 and a thermocontrol circuit (not shown) both mounted on a surface of the pressing roller 72 control halogen heaters 75 and 76, so that a surface temperature of the roller 72 is maintained at a constant value suitable for the fixing process.
The silicone oil in an oil pool is removed to an oil application roller 77 through an oil pump-up roller 78 for sequentially controlling the oil application roller 77 to contact with or separate from the fixing roller 71. Thus, a constant quantity of oil is to be held on the fixing roller 71 by an oil control blade 80.
Cleaning devices 73 and 74 utilize zonal cleaning web members to attain an excellent cleaning with maintaining their fresh surfaces by drawing out and rolling up the web members.
In case of forming a full-color image on a transparent recording material, it is preferable to increase a fixing set temperature, to decrease a fixing feed speed or to increase a fixing pressure, as compared with a case of fixing a reflect recording material. This is because the sufficient heat is added so as not to remain the grain form of each color toner in the recorded image holding layer on a PET sheet. In order to realize such an operation, a means for delaying the fixing feed speed is generally used under a consideration of a waiting time for switching with the reflect recording material and a structural arrangement of the hardware.
However, if the fixing speed is set suitably for the transparent recording material, it is appeared an area at which a pulse motor cannot uniformly be driven. Further, since heat to be given to a PET sheet becomes unexpectedly large, the transparent recording sheet passes through feed rollers 81 in a thermoplastic state after passing through the fixing roller 71. As a result, there occurs such a defect as the surface of a transparent recording sheet becomes worse.
It should be noted that, since probability that the fused toner adheres to the fixing roller becomes large in an area where a great deal of toner is transferred at a high concentration (or density) area of an image, there occurs such an image defect as the density of the high concentration area becomes thin. Moreover, the transparent recording sheet becomes likely to entwine around the fixing roller because of the tackiness of the fused toner. If the sheet entwines around the fixing roller, a serious damage will be occurred in an image forming apparatus.